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Area Forecast Discussion

514
FXUS64 KHUN 291116 AAA
AFDHUN

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HUNTSVILLE AL
616 AM CDT FRI AUG 29 2014

.UPDATE...
FOR 12Z TAFS

&&

.DISCUSSION...
/ISSUED 522 AM CDT FRI AUG 29 2014/
ANALYSIS OF EVENING SOUNDING DATA AND WV SATELLITE IMAGERY INDICATE
THAT A SEASONABLY STRONG MID-LEVEL RIDGE REMAINS CENTERED ACROSS
THE SOUTHEASTERN ATLANTIC COAST THIS MORNING...AND THIS FEATURE IS
EXPECTED TO REMAIN IN PLACE TODAY AND TONIGHT. FURTHER UPSTREAM...A
WEAK 500-MB SHORTWAVE TROUGH CURRENTLY ACROSS THE CENTRAL PLAINS IS
PROGGED TO SHIFT EASTWARD ACROSS THE MISSOURI VALLEY...WITH A RATHER
STRONG BELT OF MID-TROPOSPHERIC SOUTHWESTERLY WINDS EXPECTED TO
EVOLVE WITHIN THE INCREASING HEIGHT GRADIENT BETWEEN THIS FEATURE AND
THE RIDGE TO THE SOUTHEAST. ANOTHER WEAK DISTURBANCE OVER THE LOWER
MISSISSIPPI VALLEY WILL LIFT NORTHEASTWARD ACROSS WESTERN TENNESSEE
AND KENTUCKY LATER TODAY IN THIS REGIME...BUT WITH STRONGEST FORCING
FOR UVM REMAINING WEST OF THE REGION ONLY AN INCREASE IN CIRROFORM
CLOUDS IS EXPECTED. DUE TO THE HIGH/THIN NATURE OF THE CLOUD
COVER...THIS WILL HAVE ONLY A MINOR IMPACT ON HIGH TEMPERATURES...
WITH VALUES AROUND A DEGREE OR SO COOLER THAN THOSE OBSERVED ON
THURSDAY.

FOR THE REMAINDER OF THE SHORT TERM PERIOD...GUIDANCE FROM GFS/NAM IS
IN GOOD AGREEMENT THAT THE CENTRAL PLAINS MID-LEVEL WAVE WILL SHEAR
APART AND LIFT NORTHEASTWARD ACROSS THE UPPER MISSISSIPPI
VALLEY/GREAT LAKES AND INTO SOUTHERN QUEBEC BY SUNDAY EVENING. THIS
WILL EFFECTIVELY FORCE THE SOUTHEASTERN CONUS RIDGE TO DEAMPLIFY AND
EXPAND SOUTHWESTWARD INTO THE WESTERN GULF...SETTING UP A STRONGER
SOUTHWEST FLOW ALOFT AND RICH TROPICAL MOISTURE FETCH ACROSS THE
LOCAL AREA. SHOWERS/THUNDERSTORMS WILL LIKELY BEGIN TO INCREASE FROM
THE SOUTHWEST VERY EARLY SATURDAY MORNING...AS PWATS RISE TO 2+
INCHES AND WEAK ISENTROPIC ASCENT BECOMES EVIDENT BETWEEN THE
300-320K SURFACES. ALTHOUGH SOME MODEL GUIDANCE SUGGESTS THE PASSAGE
OF A WEAK MID-LEVEL VORT MAX OVERNIGHT...IT APPEARS THAT MOST OF THE
ATMOSPHERIC LIFT WILL BE GENERATED BY VEERING WINDS/WARM ADVECTION
WITHIN THE LOWER TROPOSPHERE AND WILL KEEP POPS IN THE CHANCE RANGE
AS A RESULT. FURTHERMORE...A LINGERING WEDGE OF DRY AIR MAY LIMIT
THE NORTHEASTWARD EXTENT OF PRECIPITATION ACROSS NE ALABAMA/SRN
TENNESSEE. GLOBAL MODELS CONTINUE TO GENERATE A STRONGER
CONVECTIVELY-INDUCED VORT MAX OVER THE NW GULF COAST TONIGHT...WHICH
WILL LIKELY LIFT NORTHEASTWARD INTO THE LOWER MISSISSIPPI VALLEY AND
BEGIN TO ENHANCE RAIN CHANCES FURTHER ACROSS THE NW HALF OF THE
FORECAST AREA TOMORROW AFTERNOON. ACROSS THE SOUTHEAST HALF OF THE
AREA...INFLUENCE FROM THE SOUTHEASTERN CONUS RIDGE WILL BE STRONGER
AND HAVE REDUCED POPS INTO THE CHANCE RANGE. THIS VORT MAX IS
EXPECTED TO BECOME INCREASINGLY STRETCHED/SHEARED AS IT LIFTS
NORTHEASTWARD...BUT WILL LIKELY CONTINUE TO PROVIDE A HIGHER COVERAGE
OF SHOWERS/STORMS FOR THE NW HALF OF THE AREA ON SATURDAY
NIGHT/SUNDAY MORNING. CONDITIONS WILL IMPROVE FOR ALL LOCATIONS BY
SUNDAY AFTERNOON...AS THE REMNANTS OF THE WAVE LIFT NORTHEASTWARD
AWAY FROM THE AREA. THICK CLOUDS WILL KEEP HIGHS IN THE MID 80S
TOMORROW...WITH LOWER 90S POSSIBLE SUNDAY AFTERNOON AS CLOUDS
DIMINISH. LOWS SATURDAY/SUNDAY MORNINGS WILL BE IN THE UPPER
60S/LOWER 70S.

SOUTHWEST FLOW ALOFT WILL PERSIST ACROSS THE CENTRAL TENNESSEE
VALLEY ON SUNDAY NIGHT...WITH THE POTENTIAL FOR ANOTHER DISTURBANCE
WARRANTING A LOW CHANCE POP AT THIS TIME. HOWEVER...CONDITIONS WILL
BEGIN TO CHANGE FROM MONDAY THROUGH THE REMAINDER OF THE EXTENDED
PERIOD...AS THE SUBTROPICAL RIDGE EXPANDS WESTWARD TO ENCOMPASS MOST
AREAS FROM THE SOUTHERN PLAINS TO THE SOUTHEASTERN ATLANTIC COAST.
FORECAST SOUNDINGS SUGGEST THAT PWATS WILL FALL INTO THE 1.4-1.6 INCH
RANGE DURING THIS PERIOD...AND WITH NO CLEAR EVIDENCE OF SYNOPTIC
SCALE FORCING FOR UVM EXPECT ONLY ISOLATED DIURNAL CONVECTION AT
BEST. HIGH TEMPERATURES WILL WARM BACK INTO THE LOWER/MID 90S...BUT
DEWPOINTS WILL BE MUCH HIGHER THAN WHAT WE HAVE EXPERIENCED FOR THE
PAST COUPLE OF DAYS -- LEADING TO HEAT INDEX VALUES IN THE 100-105
DEGREE RANGE.

70/DD

&&

.AVIATION...
FOR 12Z TAFS...

VFR CONDITIONS ARE EXPECTED TO CONTINUE ACROSS N AL/S MIDDLE TN FOR
THE NEXT 24 HOURS. -SHRA/-TSRA ARE POSSIBLE CLOSE TO THE END OF THE
PERIOD (AROUND 10-12Z) AND HAVE NOT INCLUDED IN TAF AT THIS TIME DUE
TO SPATIAL COVERAGE AND INITIAL DEVELOPMENT UNCERTAINTY.

SL.77

&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...NONE.
TN...NONE.
&&

$$

FOR MORE INFORMATION PLEASE VISIT OUR WEBSITE
AT WEATHER.GOV/HUNTSVILLE.



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